An image forming optical system comprising four or five lens groups in total, wherein during zooming from the wide angle end to the telephoto end, the distance between the first lens group and the second lens group increases, the distance between the second lens group and the third lens group decreases, and the distance between the third lens group and the fourth lens group changes, the first lens group comprises three lenses including a negative meniscus lens, a positive meniscus lens, and a positive lens, the second lens group includes a negative meniscus lens having a convex surface directed toward the object side and a concave surface directed toward the image side, the negative meniscus lens being located closest to the object side in the second lens group, the position of the second lens group at the telephoto end is closer to the object side than that at the wide angle end, the image forming optical system has an aperture stop that moves integrally with the third lens group, the third lens group includes a positive lens component and a negative lens component, and the fourth lens group comprises one lens.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An image forming optical system comprising four or five lens groups in total including, in order from its object side to image side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a refracting power, wherein during zooming from the wide angle end to the telephoto end, the distance between the first lens group and the second lens group increases, the distance between the second lens group and the third lens group decreases, and the distance between the third lens group and the fourth lens group changes, the first lens group comprises three lenses including a negative meniscus lens, a positive meniscus lens, and a positive lens, the second lens group includes a negative meniscus lens having a convex surface directed toward the object side and a concave surface directed toward the image side, the negative meniscus lens being located closest to the object side in the second lens group, the position of the second lens group at the telephoto end is closer to the object side than that at the wide angle end, the image forming optical system has an aperture stop that moves integrally with the third lens group, the third lens group includes a positive lens component and a negative lens component, and the fourth lens group consists of one lens.
2. The image forming optical system according to claim 1 , wherein the first lens group is located closer to the object side at the telephoto end than at the wide angle end.
3. The image forming optical system according to claim 1 , wherein the negative meniscus lens in the first lens group is located closer to the object side than the positive meniscus lens in the first lens group, the image side surface of the negative meniscus lens in the first lens group has a paraxial radius of curvature that is smaller in the absolute value than that of the object side surface thereof, and the image side surface of the positive meniscus lens in the first lens group has a paraxial radius of curvature that is larger in the absolute value than that of the object side surface thereof.
4. The image forming optical system according to claim 1 , wherein both the negative meniscus lens and the positive meniscus lens in the first lens group are meniscus lenses that are convex toward the object side.
5. The image forming optical system according to claim 1 , wherein the negative meniscus lens and the positive meniscus lens in the first lens group are cemented together.
6. The image forming optical system according to claim 1 , wherein the second lens group has a positive lens and a negative lens located on the image side of the negative meniscus lens.
7. The image forming optical system according to claim 1 , wherein the second lens group comprises the negative meniscus lens, the positive lens, and the negative lens.
8. The image forming optical system according to claim 1 , wherein the negative lens in the second lens group has an aspheric surface.
9. The image forming optical system according to claim 1 , wherein the third lens group is located closer to the object side at the telephoto end than at the wide angle end.
10. The image forming optical system according to claim 1 , wherein the third lens group comprises two lenses including, in order from the object side, a positive lens and a negative lens.
11. The image forming optical system according to claim 1 , wherein the third lens group comprises three lenses including, in order from the object side, a positive lens, a positive lens, and a negative lens.
12. The image forming optical system according to claim 1 , wherein the positive lens in the third lens group has a biconvex shape, and the negative lens in the third lens group has a meniscus shape with a convex surface facing the object side and a concave surface facing the image side.
13. The image forming optical system according to claim 1 , wherein both the object side surface and the image side surface of the positive lens in the third lens group are aspheric surfaces.
14. The image forming optical system according to claim 1 , wherein the image side surface of the negative lens in the third lens group is an aspheric surface.
15. The image forming optical system according to claim 1 , wherein the focusing operation from an object at a long distance to an object at a short distance is performed by moving the fourth lens group.
16. The image forming optical system according to claim 1 , wherein the fourth lens group consists of one positive lens.
17. The image forming optical system according to claim 1 , wherein the fourth lens group consists of one negative lens.
18. The image forming optical system according to claim 16 , wherein the fourth lens group consists of a meniscus lens having an aspheric surface.
19. The image forming optical system according to claim 17 , wherein the fourth lens group consists of a biconcave lens having an aspheric surface.
28. An electronic image pickup apparatus comprising the image forming optical system according to claim 1 , and an image pickup element that has an image pickup surface provided on the image side of the image forming optical system and converts an optical image formed on the image pickup surface by the image forming optical system into an electrical signal.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
April 22, 2011
November 26, 2013
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.